Chapter 17.3, Problem 18R

To determine

To Explain:The reason that the graphite is a lubricant while the diamond is the hardest gem.

Explanation of Solution

Introduction:

Diamond and graphite are the crystalline forms of the carbon atom. Both are made up of carbon-atoms alone but graphite is softer as compared to the diamond.

The distance between the carbon atom with respect to its neighbor carbon atom is equal in the diamond. Due to the rigid network of atoms, they cannot move. Hence, diamond is very hard and therefore, its melting point is high. But in the case of graphite, there are covalent bonds formed between its carbon-carbon atoms of each layer and this bond is strong but between the layers, there are very weak forces. Due to these forces between the carbon layers, graphite is softer s compared to the diamond.

Conclusion:

Graphite is very lubricant because the interaction forces between the layers of carbon-carbon atoms are very weak while the carbon atoms in the Dimond lie at the equal distances to each of its neighboring carbon atom. Therefore, diamond is hardest due to its rigid network of the carbon atom.